1. Field of the Invention
This invention relates to a process of preparing a catalyst for use in production of methacrylic acid and the catalyst and also relates to a process of preparing methacrylic acid in the presence of the catalyst, more particularly, to the process of preparing the catalyst and the same which is suitable for preparing methacrylic acid by gas phase oxidation and/or oxidative dehydrogenation of at least one compound selected from the group consisting of methacrolein, isobutyraldehyde and isobutyric acid and the process for preparing methacrylic acid in the presence of the catalyst.
2. Description of the Prior Art
There have been many proposals concerning a catalyst for preparing methacrylic acid by gas phase oxidation of methacrolein, isobutyraldehyde and unsaturated aldehyde and a process thereof. For example, in the case of using methacrolein, there have been also many proposals about improving a catalyst such as heteropoly-acids. These proposals were divided into two categories. One is concerning a composition of a catalyst and the choice of the composition and another is concerning a regulation of catalyst properties and a process thereof with good reproducibility. According to the later, for example, it is described that the preferred specific surface area of a catalyst ranges from 0.01 to 5 m.sup.2 /g and 0.01 to 50 m.sup.2 /g in Japan Open-Laid No.49-116022 and Japan Open-Laid No.50-37710, respectively. In spite of these specification, this catalyst is not suitable for industrial use because of excessively high reaction temperature and low selectivity.
Many proposals concerning the control of pore structure of a catalyst have been done. For example, Japan Open-Laid No.51-136615 and Japan Open-Laid No.55-73347 propose a catalyst which is achieved by adding organic substances such as multivalent alcohol and polyvinyl alcohol and then curing them. However, the organic substances, which is used as additive and has a high decomposition temperature, will burn by heat treatment and thereby cause sintering and reduction of a catalyst and a problem such as low reproducibility of a catalyst still remains. Japan Open-Laid No.4-367737 proposed a process, wherein an organic polymer such as polymethylmethacrylate and polystyrene, which decomposes into a monomer and vaporizes at a relatively low temperature, is added, this method is also insufficient in the reproducibility of a catalyst.
In addition, a molding process, where a dried powder containing catalytic composition with the particle size adjusted in the range of 1 to 250 .mu.m is used as a raw material, was proposed for the preparation of a catalyst in Japan Open-Laid 8-10621. However this process is not insufficient for industrial use, since this process has a problem of low reproducibility and also needs a more complicated drying process.
A catalyst for industrial use is generally used as a molded article. A molded article is produced by the process such as press molding, extrusion molding, rolling molding, Marumerizer molding, fluidized granulation, centrifuge fluidized coating process and the like. However, it is very hard to mold without lowering performance of a catalyst, and performance of the obtained catalyst is usually insufficient in reproducibility. For example, examples using press molding process were disclosed in Japan Open-Laid No.63-315148, Japan Open-Laid No.8-10621, Japan Open-Laid No.10-258233 and Japan Patent Gazette No.3-58776. According to all examples of them, a process of a press molding was not investigated in detail and these disclosures were insufficient from the view point of the reproducibility.